Incorporation of Carbon in Free-Standing HVPE-Grown GaN Substrates

Abstract

Carbon doping is a viable approach for compensating the unintentional donors in GaN and achieving semi-insulating substrates necessary for high-frequency, high-power devices. In this work, bulk material properties and point defects are studied in mm-thick free-standing carbon-doped GaN to understand the efficacy of the carbon dopant. Temperature-dependent Hall measurements reveal high resistivity and low carrier concentrations at temperatures as high as 560°C in a 6 × 1017 cm−3 C-doped sample, and electron paramagnetic resonance (EPR) indicates that carbon acts as the compensating defect. Photoluminescence, in agreement with photo-EPR, suggests that the compensating center is CN; however, additional defects, which possibly limit compensation, are formed at carbon concentrations greater than 5 × 1017 cm−3.